1. Field of the Invention
The present invention relates to a two-terminal paired circuit.
2. Description of the Related Art
An example of a prior art impedance circuit is shown in FIG. 1. The circuit shown in FIG. 1 is a one-terminal paired circuit in which an impedance is formed between input terminals Vin and -Vin thereof.
In the circuit shown in FIG. 1, the collector of a transistor Q1 is connected to the input terminal Vin and its emitter is grounded through a constant current source Ie. Between the input terminal Vin and the ground, there exists a bias circuit comprised of a transistor Q5 and resistors R1, R2. The base of the transistor Q1 is connected to the connecting point between the resistors R1 and R2.
A transistor Q2 is connected at its collector to the input terminal -Vin and at its emitter to the ground through a constant current source Ie. Between the input terminal -Vin and the ground, there exists a bias circuit comprised of a transistor Q6 and resistors R1, R2. The base of the transistor Q2 is connected to a connection point between the resistors R1 and R2.
An impedance element 2Z is connected between the emitters of the transistors Q1 and Q2.
Since a current Iin, which flows through the circuit, flows from the terminal Vin to the ground as shown in FIG. 1, the impedance element 2Z is connected between the sides of input terminals Vin, -Vin and the ground.
In the impedance circuit shown in FIG. 1, an impedance component seen from the input terminal Vi seems to exist between the differential pairs. Accordingly, the impedance seen from the input side can exist for the ground only. Thus, when to a certain impedance another impedance is added, they are always connected in parallel.
Therefore, it is impossible to realize such a circuit that impedances are connected in series which is indispensable to assemble a ladder-type transmission network thereinto. Accordingly, if a high Q in filtering characteristics is realized, there is only such a measure that a filter is connected in cascade with many stages or the Q is made high while the dynamic range of the circuit is scarified. As a result, the number of circuit elements is increased with the result that the characteristics are deteriorated.